The general aim of this project is to understand at a quantitative level the role of cell deformability and mechanical function in the circulation under normal and pathological conditions. The broad interests of the PI's encompass the function of red blood cells, neutrophils and immortalized cell lines thought to mimic the behavior of these cells. This project focusses on the properties and function of cells from the erythroid lineage. Studies of the mechanical aspects of neutrophil adhesion are proposed with Project 1. The areas of investigation involving red cells (this project) range from cell maturation and bone marrow egress to senescence and disappearance of cells from the circulation. Changes in cell dimensions are properties during red cell maturation and aging under normal conditions in vivo will be measured in collaboration with Dr. M. Snyder (UMASS Medical Center, Boston, MA) using the baboon as a model system. In addition, the effects of well-defined cellular mechanical abnormalities on cell survival and flow in the microcirculation will be measured in the mouse to establish the tolerable limits for abnormal deformability and the consequences of abnormal deformability on microcirculatory blood flow. In pursuing these investigations, Dr. Knauf will develop strategies for altering and stabilizing cell volume, and Dr. Waugh will measure the results of these and other modifications on cell dimensions and mechanical properties. In collaboration with Project 5 (Dr. Cokelet) the effects of altered deformability on cell distribution in model networks in vitro will be established, and in cooperation with Project 4 (Dr. Sarelius) the effects of these alterations on the survival and distribution of these cells in the living vasculature will be determine. The importance of humoral factors and the effects of hemorrhagic stress on the development of proper red cell membrane mechanical function during late stage maturation will be assessed with particular focus on the stability of the bilayer-skeletal interface and the proper development of membrane shear elasticity. Finally, the hypothesis that changes in cell deformability during maturation are a significant factor in the regulation of cell egress from the bone marrow will be evaluated. We will take advantage of the resources at the National Nanofabrication Facility at Cornell University to obtain thin circular apertures in silicon wafers to model the geometry of the marrow endothelial pores through which the cells must pass and determine the dependence of cell passage on pore size and pressure for marrow erythroid cells of different maturities.